I was also thinking that he might eating from the bottom after food sinking. I think no matter how you try to scoop it some of it still end up on the bottom of the tank.

Also i saw a lot of people recommending try frozen blood worms.If you cook shrimp for trhe dinner you can try to give him tiny piece (size of the pellet). The bad thing that shrimp sink to the bottom right away. You can use eye dropper to feed.